There are a number of situations where hydrocarbon wells are treated by igniting a gas generator in the well and allowing the high pressure combustion products to flow into a subterranean formation intersecting the well. One such treatment is a fracturing treatment, roughly analogous to hydraulic fracturing, where the purpose is to increase the permeability of the formation adjacent the perforations. Rather than fracturing the formation and then propping it open with sand, as in hydraulic fracturing, the mechanism is that the high pressure combustion gases initiate and then erode micro and radial fractures originating from each perforation channel.
Oil and gas wells are subject to many ailments, some of which are treatable by injecting a treatment liquid into the formation. As used herein, a liquid is a material which is at a temperature above its melting point and below its boiling point and includes slurries. Examples are the injection of resins to reduce sand movement into the production string and the injection of solvents to remove asphaltenes accumulating in the zone near the well bore.
Most treatment liquids are injected into hydrocarbon bearing formations with a pump truck by a process known as bullheading, i.e. a truck drives up to the well and pumps the treatment liquid down the production string into the formation. The treatment liquid automatically follows the path of least resistance and enters the zones with the highest permeability. The treatment liquid is usually followed with a chaser liquid that displaces the treatment liquid from the production string so all of the treatment liquid is delivered into the formation. This is a time honored practice that has the advantages of simplicity, low costs, and predictable results provided the zones are very thin and homogenous.
There are some situations where more sophisticated and more expensive means of injecting treatment liquids have been proposed and used. One type of approach is to place the treatment liquid in the well and ignite a gas generating propellant in the production string, as shown in U.S. Pat. Nos. 2,740,478; 4,936,385; 5,101,900; 5,145,013 and 5,443,123. Of more general interest is the disclosure in U.S. Pat. No. 3,029,732.
It is known in the prior art to ignite a gas generating charge and create relatively low pressure gaseous combustion products for the purpose of stimulating a well by cleaning out the perforations in production casing or cleaning out the slots in a slotted liner. Examples are found in U.S. Pat. Nos. 4,064,935 and 4,081,031.